The present invention relates generally to a combustor for a gas turbine engine having water injection for NOx abatement and, in particular, to a venturi in the swirl cup package for such combustor which is configured to have a thickness from an upstream end to a downstream end that provides a heat transfer conduction path and reduces axial stresses imposed thereon.
It is well known that the combustor of a gas turbine engine is subjected to extreme temperatures during operation, perhaps as high as 3500.degree. F. Accordingly, several measures have been employed in the art to protect combustor components against thermal shock and high thermal stresses. These include the use of new and exotic metal alloys, various heat shield configurations, cooling schemes and certain types of thermal barrier coatings as demonstrated by U.S. Pat. No. 5,553,455 to Craig et al., U.S. Pat. No. 5,528,904 to Jones et al., U.S. Pat. No. 5,220,786 to Campbell, U.S. Pat. No. 4,655,044 to Dierberger et al., and U.S. Pat. No. 4,567,730 to Scott.
Another consideration involved with the design of gas turbine combustors is the ability to minimize emissions therefrom. In the case of marine and industrial applications, this has typically been accomplished through the injection of water into the combustor to reduce the temperature therein (e.g., through the nozzle circuit utilized for supplying fuel). It has been found, however, that such water injection has had the undesirable effect of causing metal distress and erosion to certain components of the combustor due to cavitation and impingement. The particular combustor components concerned may vary depending upon combustor design and exactly where impingement of the water takes place. It will be understood, however, that water is more punitive than other fluids passing through the combustor, such as liquid fuel and steam, because it has a higher coefficient of convective heat transfer and, all else being equal, causes higher thermal stress.
While some attempts have been made to solve both the thermal and erosion problems set forth above, such as in the Campbell patent, it will be noted that the venturi therein has an "extended" design, meaning it has an axial length from an upstream end adjacent the swirler to a downstream end adjacent the downstream end of the swirl cup spaced radially about the venturi. While this extended venturi design helps minimize water erosion of the dome components by releasing the water further downstream, it has been found that the fuel exiting the venturi with the water is so close to the igniter location as to make light-off for liquid fuel very difficult. Moreover, it will be appreciated that the three-piece welded assembly of the swirler, venturi and heat shield in the '786 patent is more expensive than desired.
It will also be recognized in a previously filed application by the assignee of the present invention, entitled "Method Of Protecting Gas Turbine Combustor Components Against Water Erosion And Hot Corrosion," Serial No. 09/070,053, that a swirl cup package is disclosed in which a dense vertically cracked thermal barrier coating is applied to selected portions thereof subjected to water impingement. A short, thick venturi is depicted therein which has such thermal barrier coating located at a downstream portion thereof since the cone emanating from the fuel nozzle strikes this area for that particular application.
Thus, in light of the foregoing, it would be desirable for an improved venturi design to be developed which protects against axial stresses imposed thereon stemming from thermal gradients created by water injection into the combustor. It would also be desirable to minimize the number of components forming the swirl cup package, as well as reduce the cost of manufacturing it.